The disclosure relates generally to determining propagation delays in a wireless distribution system (WDS), such as a distributed antenna system (DAS) and, more particularly to determining downlink and uplink propagation delays that may be asymmetric.
Wireless customers are increasingly demanding digital data services, such as streaming video signals. At the same time, some wireless customers use their wireless communications devices in areas that are poorly serviced by conventional cellular networks, such as inside certain buildings or areas where there is little cellular coverage. One response to the intersection of these two concerns has been the use of WDSs. WDSs include remote units configured to receive and transmit communications signals to client devices within the antenna range of the remote units. WDSs can be particularly useful when deployed inside buildings or other indoor environments where the wireless communications devices may not otherwise be able to effectively receive radio frequency (RF) signals from a source.
In this regard, FIG. 1 illustrates distribution of communications services to remote coverage areas 100(1)-100(N) of a WDS 102, wherein ‘N’ is the number of remote coverage areas. These communications services can include cellular services, wireless services, such as RF identification (RFID) tracking, Wireless Fidelity (Wi-Fi), local area network (LAN), and wireless LAN (WLAN), wireless solutions (Bluetooth, Wi-Fi Global Positioning System (GPS) signal-based, and others) for location-based services, and combinations thereof, as examples. The remote coverage areas 100(1)-100(N) may be remotely located. In this regard, the remote coverage areas 100(1)-100(N) are created by and centered on remote units 104(1)-104(N) connected to a head-end equipment (HEE) 106 (e.g., a head-end controller, a head-end unit, or a central unit). The HEE 106 may be communicatively coupled to a signal source 108, for example, a base transceiver station (BTS) or a baseband unit (BBU). In this regard, the HEE 106 receives downlink communications signals 110D from the signal source 108 to be distributed to the remote units 104(1)-104(N). The remote units 104(1)-104(N) are configured to receive the downlink communications signals 110D from the HEE 106 over a communications medium 112 to be distributed to the respective remote coverage areas 100(1)-100(N) of the remote units 104(1)-104(N). In a non-limiting example, the communications medium 112 may be a wired communications medium, a wireless communications medium, or an optical fiber-based communications medium. Each of the remote units 104(1)-104(N) may include an RF transmitter/receiver (not shown) and a respective antenna 114(1)-114(N) operably connected to the RF transmitter/receiver to wirelessly distribute the communications services to client devices 116 within the respective remote coverage areas 100(1)-100(N). The remote units 104(1)-104(N) are also configured to receive uplink communications signals 110U from the client devices 116 in the respective remote coverage areas 100(1)-100(N) to be distributed to the signal source 108. The size of each of the remote coverage areas 100(1)-100(N) is determined by amount of RF power transmitted by the respective remote units 104(1)-104(N), receiver sensitivity, antenna gain, and RF environment, as well as by RF transmitter/receiver sensitivity of the client devices 116. The client devices 116 usually have a fixed maximum RF receiver sensitivity, so that the above-mentioned properties of the remote units 104(1)-104(N) mainly determine the size of the respective remote coverage areas 100(1)-100(N).
With reference to FIG. 1, the client devices 116 transmit the uplink communications signals 110U to signal source 108 via the remote units 104(1)-104(N), the communications medium 112, and the HEE 106. Accordingly, the uplink communications signals 110U may experience an uplink propagation delay when arriving at the signal source 108. The signal source 108 may be configured to accommodate for the uplink propagation delay associated with the uplink communications signals 110U by assigning timing advance(s) (TA(s)) to the client devices 116. In addition, a geo-location server 118 may be included in the WDS 102 to determine locations of the client devices 116 based on the uplink propagation delay.
As mentioned above, the communications medium 112 may be a non-wireless communications medium, such as an electrical conductor communications medium, or an optical fiber-based communications medium. As such, the uplink communications signals 110U may experience different propagation delays traveling through the communications medium 112 as opposed to a wireless medium. For example, the uplink communications signals 110U propagate wirelessly over the air at a speed of approximately 3.3 nanoseconds (ns) per meter (m) (3.3 ns/m). In contrast, if the communications medium 112 in the WDS 102 is an optical communications medium, the uplink communications signals 110U propagate in the WDS 102 over the uplink communications medium 110U at a speed of approximately five (5) ns per meter (5 ns/m). However, the signal source may not be aware of the WDS 102. As a result, if the signal source 108 assumes that the uplink communications signals 110U are received over a wireless communications medium while the uplink communications signal 110U is in fact received over a non-wireless communications medium, for example, the signal source 108 may end up assigning inappropriate TA(s) to the client devices 116. Likewise, the geo-location server 118 may also determine inaccurate locations for the client devices 116. Hence, it is desired to accurately determine downlink and uplink propagation delays associated with the communications medium 112.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.